114 bulletin: museum of comparative zoology. 



the neighboring body. At a Httle later stage (Fig. 204) the spermatid 

 has become much elongated and an axial filament is present. I have 

 been unable to find, at this time, any trace of a centrosome, but the 

 axial filament appears to be attached directly to the nuclear membrane 

 at a point nearly, or quite, 90° from the Nebenkern. The small, 

 less deeply staining body which was formerly applied to the nuclear 

 membrane near the Nebenkern can no longer be distinguished. Prob- 

 ably it has become converted into the homogeneous envelope which 

 surrounds the axial filament. 



The Nebenkern now presents a very striking appearance, since one 

 side stains intensely with hematoxylin. However, the staining quali- 

 ties of the Nebenkern during this and later stages appears to be 

 dependent on the quality of the fixation. While one side of the 

 Nebenkern stains deeply in spermatids exhibiting the best fixation, — - 

 e. g. those lying near the follicular wall, — in the case of spermatids 

 less perfectly fixed the stain is less intense, or may be absent altogether. 

 Also, in material fixed in Worcester's formol sublimate-acetic fluid 

 the Nebenkern stains lightly or not at all. 



The chromatin continues to disintegrate into finer granules, although 

 the monosome still retains its characteristic structure. Somewhat 

 later (Fig. 205) the finely granular chromatin is coljected around the 

 periphery of the nucleus, while at the center there is a lighter region 

 apparently free from chromatin. However, the peripheral distribu- 

 tion of the chromatin persists only a short time, for a little later it is 

 seen to occupy the anterior end of the nucleus, while at the posterior 

 end there is a lighter region (Fig. 206). The chromatin, including 

 the monosome, has now become converted into very fine granules, 

 which stain with hematoxylin less deeply than formerly, so that, as in 

 Dissosteira, the nucleus as a whole stains grayish. The nucleus now 

 rotates through an angle of about 90° and at the same time two minute 

 deeply staining centrosomes appear at the proximal end of the axial 

 filament, where it is attached to the nucleus. I have not been able 

 to determine the origin of these centrosomes nor whether, indeed, they 

 lie within or without the nuclear membrane, to which they are closely 

 applied. Meanwhile, the Nebenkern begins to migrate toward the 

 anterior end of the nucleus. The deeply staining portion has now 

 spread over one side of this body, so that about one half of the surface 

 of the Nebenkern is seen to be enveloped by a deeply staining cap. 

 In Figure 207 the deeply staining cap has extended over the entire 

 surface of the Nebenkern, which has now become applied to the an- 

 terior end of the nucleus. The further changes in the spermatids 



